From: John De Armond
Subject: Re: Need to Pick your Brains (Gunshot Residue Forensics)
Organization: Dixie Communications Public Access.  The Mouth of the South.

pyro@strauss.udel.edu (Thomas Rich Schwerdt) writes:

#If the police/BATF/whoever decides to do extensive testing, they can detect
#incredibly minute traces of explosives residue, or powder residue.  I do not
#have the source on hand, but I read a study where the subjects washed their
#hands on the order of 20 times with soap and water, and the explosives traces
#were still easily detectable on the hands.,
#In almost any of the scenarios described (shaking hands with a person who
#had been shooting, being near a shotgun blast, washing hands multiple times)
#I would expect the residues to be quite detectible.
#How to "beat" the tests? Go shooting at the range with a few friends. You now
#have a great reason for having powder residue all over yourself, and an alibi
#to prove it.

Or just do something such as handling fertilizer which will legitimately
put nitrates on your hands, since all the tests I'm aware of look for
nitrogen or nitrates.  Among the ones that come immediately to mind:

* neutron activation analysis - among the most sensitive.  Involves
	nuking the sample with neutrons and then looking for the characteristic
	gamma rays and decay rate of N-16.  Can be adopted for field use, though
	the greater the neutron flux, the higher the sensitivity.  The most
	sensitive tests use nuclear reactors for the neutron source.  A
	variation of this is used in the so-called thermal neutron bomb
	detectors the FAA has been trying to force down the throat of
	the airline industry.  Easily defeated by wrapping the explosive
	in cadmium foil.

*	Ion drift detector - technology used in airport and nuclear plant
	bomb sniffers.  Pretty damn sensitive.  I've seen nuclear plant
	detectors detect a nitroglycerin patche on a person walking by.
	Also had one trip on the powder residue on my shooting jacket from
	the day before.

*	Mass spectrometer - separates a sample according to its atomic
	or molecular weights.  Probably the most sensitive, can count atoms.
	Also very expensive.

*	Chromatography - the various versions separate the sample into
	constituent parts using differential absorption (gas), diffusion rate
	(liquid) or electrochemical (electrophoresis).  Moderate sensitivity
	but fairly cheap to do.

Anything I missed, Tom?

John